3 research outputs found
New Insights into Structure and Luminescence of Eu<sup>III</sup> and Sm<sup>III</sup> Complexes of the 3,4,3-LI(1,2-HOPO) Ligand
We
report the preparation and new insight into photophysical properties
of luminescent hydroxypyridonate complexes [M<sup>III</sup><b>L</b>]<sup>â</sup> (M = Eu or Sm) of the versatile 3,4,3-LIÂ(1,2-HOPO)
ligand (<b>L</b>). We report the crystal structure of this ligand
with Eu<sup>III</sup> as well as insights into the coordination behavior
and geometry in solution by using magnetic circular dichroism. In
addition TD-DFT calculations were used to examine the excited states
of the two different chromophores present in the 3,4,3-LIÂ(1,2-HOPO)
ligand. We find that the Eu<sup>III</sup> and Sm<sup>III</sup> complexes
of this ligand undergo a transformation after in situ preparation
to yield complexes with higher quantum yield (QY) over time. It is
proposed that the lower QY in the in situ complexes is not only due
to water quenching but could also be due to a lower degree of f-orbital
overlap (in a kinetic isomer) as indicated by magnetic circular dichroism
measurements
Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1âHydroxypyridin-2-one Complexes in Aqueous Solution
A series of 10 tetradentate 1-hydroxy-pyridin-2-one
(1,2-HOPO)
ligands and corresponding eight-coordinated photoluminescent EuÂ(III)
and SmÂ(III) complexes were prepared. Generally, the ligands differ
by the linear (nLI) aliphatic linker length, from 2 to 8 methylene
units between the bidentate 1,2-HOPO chelator units. The photoluminescent
quantum yields (Ί<sub>tot</sub>) were found to vary with the
linker length, and the same trend was observed for the EuÂ(III) and
SmÂ(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Ί<sub>tot</sub>xΔ).
The change in ligand wrapping pattern between 2LI and 5LI complexes
observed by X-ray diffraction (XRD) is further supported by density
functional theory (DFT) calculations. The bimodal Ί<sub>tot</sub> trends of the EuÂ(III) and SmÂ(III) complexes are rationalized by
the change in ligand wrapping pattern as the bridge (<i>n</i>LI) is increased in length
Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1âHydroxypyridin-2-one Complexes in Aqueous Solution
A series of 10 tetradentate 1-hydroxy-pyridin-2-one
(1,2-HOPO)
ligands and corresponding eight-coordinated photoluminescent EuÂ(III)
and SmÂ(III) complexes were prepared. Generally, the ligands differ
by the linear (nLI) aliphatic linker length, from 2 to 8 methylene
units between the bidentate 1,2-HOPO chelator units. The photoluminescent
quantum yields (Ί<sub>tot</sub>) were found to vary with the
linker length, and the same trend was observed for the EuÂ(III) and
SmÂ(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Ί<sub>tot</sub>xΔ).
The change in ligand wrapping pattern between 2LI and 5LI complexes
observed by X-ray diffraction (XRD) is further supported by density
functional theory (DFT) calculations. The bimodal Ί<sub>tot</sub> trends of the EuÂ(III) and SmÂ(III) complexes are rationalized by
the change in ligand wrapping pattern as the bridge (<i>n</i>LI) is increased in length